1. Field of the Invention
The present invention relates to a display device, and more particularly to an active matrix type liquid crystal display device having a substrate on which switching elements are arranged in a matrix array for respective pixels.
2. Description of the Related Art
An active matrix type liquid crystal display device arranges switching elements which are represented by thin film transistors (also referred to as TFT hereinafter) on an insulation substrate made of glass or the like in a matrix array and displays videos (or images) by selecting respective pixels by the switching elements.
That is, the liquid crystal display device basically adopts a display principle which makes use of a so-called light shutter operation in which one of two substrates is used as an active matrix substrate, a liquid crystal layer is sandwiched between the active matrix substrate and another substrate on which color filters are formed, and a quantity of light which passes through the liquid crystal layer is adjusted by controlling the orientation direction of molecules of the liquid crystal layer by applying electric fields to the liquid crystal layer in response to gray scales of the pixels. Further, as a method which can enlarge a viewing angle of the liquid crystal display device, there has been developed a lateral electric field type (also referred to as IPS) liquid crystal display device in which the direction of an electric field applied to a liquid crystal layer is made substantially parallel to a surface of a substrate.
In the liquid crystal display device adopting the IPS method, TFTs are provided at respective crossing portions where gate lines (also referred to as scanning signal lines) and drain lines (also referred to as data signal lines or video signal lines) cross each other on an active matrix substrate. Further, counter electrodes which face pixel electrodes driven by the TFTs by way of the liquid crystal layer are arranged in parallel on the active matrix substrate, an electric field which is substantially parallel to a surface of the above-mentioned substrate is generated, and the orientation direction of molecules of the liquid crystal layer is controlled by the electric field. As a literature which discloses this type of liquid crystal display device, U.S. Pat. No. 5,852,485 is named, for example.